How to Clean and Re-Grease a Stiff TeleVue
Ranger or TV-60 Helical Focuser
Tele Vue’s multi-use small refractors, the Ranger and
TV-60, have a unique drawtube-plus-helical focusing mechanism. This works well
when new, but the brass helical fine-focus ring almost always becomes stiff
after a few years’ use. In extreme cases, the helical focuser can seize
up completely.
The good news is that the focuser (probably) isn’t
broken or worn out, it’s just that the grease has dried out and become
too sticky and viscous. To fix it, you just have to dissemble and clean it,
then re-grease.
It’s a straightforward job that takes perhaps an hour,
but you have to be careful and work cleanly to avoid getting grease on parts
that won’t appreciate it. Also, some of the parts are tiny: be careful
not to lose them!
What You Need
·
A
rag and white spirit or equivalent for removing grease
·
A
1/16 Allen key
·
a
7/64 Allen key
·
Light
automotive grease (I believe special focuser grease is available, but I
haven’t tried it).
How To Do It
Note: Each step refers to the image(s) above it
Step 1: Remove the nylon thumb screws in the end of the
focuser tube that hold the eyepiece or diagonal. You have to do this to
disassemble the focuser.
Step 2: loosen the two tiny grub screws that hold the
end-ring for the focuser in place. To do this, use a 1/16 Allen key. These are
tiny screws - put them in a little zip lock bag so you don’t lose ‘em.
Step 3: Unscrew the focuser end cap and remove it.
Step 4: Remove the thin plastic washer/shim from the end of
the brass focuser ring.
Step 5: Unthread the brass focuser ring that has the helical
groove inside it.
Step 6: Remove the thin plastic washer/shim from the other end
of the brass focuser ring.
Step 7: Use a 7/64 Allen key to undo the small bolt in the
slot that guides the inner focuser drawtube. Again, carefully put it aside.
Step 8: Pull the inner focuser drawtube out from the end of
the main drawtube.
Step 9: Clean everything thoroughly to remove the old grease.
Do this with a rag and white spirit, then hot water, detergent and a
toothbrush. Dry everything thoroughly.
Step 10: Re-grease sparingly with light automotive grease and
re-assemble. Adjust the stiffness of the helical focus with the tension on the
outer ring. Once you’ve got it right, the grub screws are meant to hold
the ring at that tension, but tighten them carefully to avoid moving the ring
as you do it and inadvertently changing the tension.
The focuser should now move freely and smoothly.
Note that I did this with a Ranger, but the same process
should work for a TV-60 focuser:
